A typical rotating electrical machine (for example, a synchronous electric motor) will be described below with reference to FIG. 6. The rotating electrical machine has a rotator 80 that is supported rotatable about an axis inside a housing 92; and a stator 86 that fixedly set up an outer periphery of the rotator 80 forming a gap (an air gap) 2 therebetween. The synchronous electric motor is disclosed in Jpn. Pat. Appln. Laid-Open Publication No. Hei 6-343250, the entire content of which is incorporated herein by reference, for example.
The rotator (for example, a salient pole type rotator) 80 has: a main shaft 82 that coaxially extends with an axis of a rotation, and supported rotatable about an axis by sliding bearings 94; and magnetic poles 84 that are attached to the outer periphery of abbreviated an intermediate part of the main shaft 82. Each of the magnetic poles 84 has: a pole body 84a that is attached to the outer periphery of the main shaft 82; a pole head 84b that is fixed to an outer periphery of the pole body 84a; and a rotator coil 84c that is wound around the pole body 84a. The saliency type rotator is disclosed in Jpn. Pat. Appln. Laid-Open Publication No. Hei 10-322947, the entire content of which is incorporated herein by reference, for example.
On the other hand, the stator 86 has: a stator core 88 that is fixedly set up at the outer periphery of the magnetic poles 84 (more specifically, the outer periphery of the pole heads 84b); and a stator coil 90 that is wound around the stator core 88.
Here, the width of the air gap 2 formed between the rotator 80 and the stator 86 has influence on operating characteristics of the rotating electrical machine. Therefore, when the rotating electrical machine has been assembled or maintained, there was a need to set the width of the air gap 2 at a predetermined value by measuring the width of the air gap 2 with a taper gage (by an air gap measurement).
In the air gap measurement, an operator inserts the taper gage into the housing 92 from an opening and closing section 96 formed at an axial end of the housing 92. Then, the taper gage is inserted into the housing 92 along the main shaft 82 in the direction of the arrow 100 shown in FIG. 6. The taper gage is then inserted into the axial end of the air gap 2.
However, it is hard for the operator to measure, because the distance from the opening/closing section to the air gap 2 is long. For this reason, an experienced operator is required for the measurement of high precision. And it takes a long time to measure. In addition, because the operator puts one's hand into the housing 92 from the opening/closing section 96 and measures, it is not safe.